Re: automotive alternators, three phase, RSG

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

comments interspersed... liberal snipping to keep the bandwidth down..

Subject: Re: automotive alternators, three phase, RSG
> Original poster: "Eric Davidson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <edavidson-at-icva.gov>

> Jim et al,
>
> The automotive alternator would be a good way of generating 3 phase
current.
> But there are several considerations that need to be addressed.  The
voltage
> would have to be stepped up to power a NST, and while a 12/120 volt
> transformer is easy to come by,

An alternator will put out 120 volts easily, if you run the field current up
and have the rotational speed high enough.  Example.  The alternator puts
out 14 volts (roughly) with the engine just off idle (at, say 1500 RPM).
Voltage is roughly proportional to speed if you keep the field current
constant (because V is proportional to dB/dt, and that is proportional to
speed), so at an engine speed of 6000 RPM, you should be able to get 4 times
the voltage out, i.e. around 80 volts.  In practice, run a bit more field
current, and you can get 120 V out.  Sure, the windings weren't really
designed for this voltage (sure as heck the diode bridge isn't, btw) and you
might be running a bit more field current than normal, but, on the other
hand, you aren't running it in an engine compartment next to a hot engine at
180F.


you will have to find some way to get the
> output frequency of the alternator at least close to 60 Hz.

frequency isn't critical (except, as I mentioned, the series L of the NST
will limit the current)  60 Hz transformers work find at 200 Hz (a bit more
loss in the core, but overall, just fine).

  Another issue
> is the power output.  Most alternators put out less than 100 amperes at
> 12-14 volts (only 1200-1400 watts) not too shabby for an alternator, but
far
> short of  *pole pig power*.

100A at 100V is 10kW...  current is limited mostlty by winding resistance,
and the max field current (and probably more important, your "prime mover")


  Putting several alternators in parallel,
> especially if they are dissimilar (likely,  from a pick your part
junkyard)
> would be very challenging.

I wouldn't even attempt this.. perhaps if I were rectifying it all to DC,
but the shafting, etc. is a big enough problem.

The issue of a suitable motor to drive the
> alternator must be addressed.  A 2-3 hp motor would be required.  A couple
> hundred dollar expense if you have to actually buy one.

True enough, the idea is based on scrounging stuff.  A bigger problem is
going to be rotational speed.  You want the alternator spinning around
8000-10,000 rpm (the alternator pulley on my car is a lot smaller than the
crank pulley that drives it), and a run of the mill electric motor is going
to max out at 1750 RPM. Pulleys might be the way to go, but, as Eric points
out,  you probably don't want to try and run many kW.  I was thinking that a
1/2-1HP motor from a washing machine might be a good start (since I think I
have one)


The correct speed
> must be determined (for 60 Hz output) and supplied via some sort of
pulleys
> or the like.   The most complex task will most likely be voltage
regulation,
> not easy for a wildly varying load like a Tesla coil with its spark gaps
> etc. Hope this helps. Coil safe

What voltage regulation, just let it rip...   The idea of having the rotary
gap on the same shaft for the alternator means that the gap timing will
always be perfect.  No need for 60 Hz

Actually, a 5-7 HP gasoline engine driving it might be more fun.   Then
you'd have an actual throttle for your TC.


>
> Eric